The present invention relates to a device and method for treating ischemic heart disease and, more particularly, to a coronary sinus stent and to surgical methods for implanting same. Specifically, the present invention involves implantation of the stent in the coronary sinus as a means of treating patients suffering from, for example, diffuse coronary artery disease, especially in cases where conventional balloon catheterization, bypass surgery and drugs are infeasible or ineffective treatment methods.
Blood arrives at the heart muscle via coronary arteries which begin as vessels with a diameter of several millimeters and branch progressively to smaller and smaller vessels in order to supply all the cells of the heart muscle. Blood arriving at the heart carries oxygen and nutrients which are exchanged for carbon dioxide and other wastes produced by cellular respiration. The carbon dioxide carrying blood leaves the heart muscle via a system of coronary veins which begin as small vessels and progressively merge into larger vessels. As in other organs, the veins are approximately parallel to the arteries, although the blood flow therein is in the opposite direction. The coronary veins terminate in a reservoir referred to as the coronary sinus, which, in turn, drains into the right atrium where it mixes with venous blood from peripheral organs. Venous blood is pumped from the right atrium into the pulmonary arteries which perfuse the lung and facilitate an exchange of gases, with carbon dioxide being replaced with oxygen.
In cases where the supply of blood flowing to the heart muscle via the coronary arteries is insufficient, oxygenation of the muscle tissue of the heart is reduced, producing a condition known as cardiac ischemia. Ischemia can result in atrophy and or necrosis of tissue. In the case of cardiac ischemia, this atrophy or necrosis reduces heart function and adversely affects the blood supply to the remainder of the body. Patients suffering from cardiac ischemia typically suffer from chest pains and difficulty in breathing. Cardiac ischemia may precipitate a heart attack in some cases.
Cardiac ischemia is most often caused by atherosclerosis or other conditions which block one or more coronary arteries. Current treatment options include balloon catheterization, bypass surgery and treatment with drugs. Balloon catheterization and bypass surgery are only feasible options if the coronary artery blockage exists in a small number of discrete locations, usually in fairly large blood vessels.
Balloon catheterization involves insertion of a catheter with an inflatable tip via a peripheral blood vessel into the affected coronary artery. The procedure is performed with the aid of a visualization (imaging) device (e.g., ultrasound, X-ray, fluoroscopy) which shows the catheter tip and the coronary artery occlusion. When the tip is in proximity to the occlusion, it is inflated, thereby widening the artery and releasing the occlusion. In cases, the balloon catheter serves for placing a stent within the artery and to extend or erect the stent to its service dimensions in a process known as stent catheterization. These procedures are often preferred by patients and doctors because it is relatively non-invasive.
Bypass surgery is an invasive procedure which involves opening the thoracic cavity and implanting a tube so as to replace or bypass an occluded portion of the coronary artery. The tube may be either artificial, or a peripheral blood vessel derived from the patient. While this method has proven efficacy, it has all of the disadvantages inherent in invasive surgery, e.g., post-surgical infection, complications with anesthesia, relatively long recovery time and high cost.
Patients with cardiac ischemia caused by blockage of many small vessels are not candidates for balloon catheterization or bypass surgery and are currently treatable only with drugs. These drugs include, for example, nitrates, β-blockers and calcium channel blockers. Unfortunately, patients treated with drugs often continue to have difficulty performing daily activities, suffer from shortness of breath and chest pains.
It has long been known that reducing the flow of blood exiting the coronary sinus can have beneficial effects on cardiac ischemia (Gross L. Blum L., Silverman G. J Exper. Med. (1937) 85:91, 1937; Robertson H. H. (1935) Am Heart. J. 10:533; Beck C. S., Leighninger D. S. (1954) Am. Heart J. 156:1226; Beck C. S., Leighninger D. S. (1955) Am. Heart J. 159:1264; Beck C. S., Leighninger D. S. (1961) Med. Tms. (NY) 89:17; Beck C. S., Leighninger D. S., Brofman B. L., Bond J. F. (1958) J. Amer. Med. Ass. 168:2110; Sandler G., Slesser B. V., Lawson C. W. (1967) Thorax 22:34). It is believed that reducing the flow of blood exiting the coronary sinus increases the blood pressure in the coronary arteries, thereby inducing the formation of new blood vessels, a process known as angiogenesis. The prior art procedure of reducing the flow of blood exiting the coronary sinus involves placement of a narrowing ring external to the coronary sinus, so as to narrow its inner diameter and thereby restrict blood flow therethrough. This procedure, however, is an open chest (thoracic) procedure, and therefore suffers all the limitations associated with such procedures, including, but not limited to, post-surgical infection, complications with anesthesia, relatively long recovery time and high cost. However, the prior art fails to teach minimal invasive means of reducing the flow of blood exiting the coronary sinus without thoracic surgery.
There is thus a widely recognized need for, and it would be highly advantageous to have, a device and method for reducing the flow of blood exiting the coronary sinus without thoracic surgery as a means of treating or preventing cardiac ischemia caused by, for example, diffuse coronary artery disease.